class Solution {
public:
    int maxProfit(vector<int>& prices) {
        if (prices.size() < 2) return 0;
        vector<vector<int>> dp(prices.size(), vector<int>(4));
        dp[0][0] = -prices[0];
        dp[0][1] = 0, dp[0][2] = 0, dp[0][3] = 0;
        for (int i = 1; i < prices.size(); i++) {
            dp[i][0] = max(dp[i - 1][1] - prices[i], dp[i - 1][3] - prices[i]);
            dp[i][0] = max(dp[i][0], dp[i - 1][0]); // dp[i][0]：持有股票
            dp[i][1] = max(dp[i - 1][1], dp[i - 1][3]); //dp[i][1]: 保持卖出股票
            dp[i][2] = dp[i - 1][0] + prices[i]; //dp[i][2]: 卖出股票
            dp[i][3] = dp[i - 1][2]; //dp[i][3]: 冷冻期
        }
        int n = prices.size();
        int result = max(dp[n - 1][1], dp[n - 1][2]);
        result = max(result, dp[n - 1][3]);
        return result;
    }
};
